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Date: Thu, 20 Dec 2012 00:35:17 +0800
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To: mjacob@freebsd.org
Subject: Re: Unmapped I/O
References: <20121219135451.GU71906@kib.kiev.ua> <50D1D2BD.80107@freebsd.org>
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On 12/19/12 10:44 PM, Matthew Jacob wrote:
> On 12/19/2012 5:54 AM, Konstantin Belousov wrote:
>> One of the known FreeBSD I/O path performance bootleneck is the
>> neccessity to map each I/O buffer pages into KVA.  The problem is that
>> on the multi-core machines, the mapping must flush TLB on all cores,
>> due to the global mapping of the buffer pages into the kernel. This
>> means that buffer creation and destruction disrupts execution of all
>> other cores to perform TLB shootdown through IPI, and the thread
>> initiating the shootdown must wait for all other cores to execute and
>> report.
>>
> About time!

yeah.. Bill Jolitz had patches for this in 92 ... that disappeared 
with him.

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